Lead screw means with half-nut engageable when in alignment with lead screw threads



March 27, 1962 HARTSHORN 3,026,549

. 8. LEAD SCREW MEANS'WITH HALF-NUT ENGAGEABLE WHEN IN ALIGNMENT WITHLEAD SCREW THREADS Filed March 51, 1958 3 Sheets-Sheet 1 IN V EN TOR.

T 3 DERlCK $.HARTSHORN ATTOR/Vly 3,026,549 EN IN March 27, 1962 D. s.HARTSHORN LEAD SCREW MEANS WITH HALF-NUT ENGAGEABLE WH ALIGNMENT WITHLEAD SCREW THREADS 5 Sheets-Sheet 2 Filed March 31. 1958 IN VEN TOR.DERICK S. HARTSHORN BY W ATTORNEY March 1962 D s. HARTSHORN 3,026, 49

LEAD SCREW MEANS WITH HALF-NUT ENGAGEABLE WHEN IN ALIGNMENT WITH LEADSCREW THREADS Filed March 31, 1958 3 Sheets-Sheet 5 I INVENTOR. DERICKS. HARTSHORN ATTOPAZY rates This invention relates to thread-chasingdevices and, more particularly, has reference to an apparatus forforming threads in a rotating work piece, which apparatus will be ofgenerally improved design as regards devices of this type previouslyconceived.

A more specific object is to provide a thread-chasing device havingnovel means for automatically initiating and terminating movement of thethreading tool and of the threading tool support means, longitudinallyof the work piece, whereby said device will be automatic in operationand will be operable to thread a plurality of like work pieces infollowing order, with a minimum of attention on the part of the machineattendant. While threading operations are being performed the machineattendant or machinist would usually remain watching the threadingoperation, as it is very rapid while using carbide tools and on shortthreads makes the cut in a matter of seconds. As the slide is snappedback at the completion of threading of a particular work piece, theoperator would shut off the control circuit. If the operator fails toshut olf control, the tool will repeat its path and thereby consume timethough making no further change in the work piece. It is thus proposedto carry out this object with minimum possibility of damage or affectingof the work, and it is further proposed that when used on a turret orengine lathe, threading operations performed by the device can becarried out as one of a series of operations carried out on the machine,so that the part would not need to be inserted in the machine forthreading only.

Another object is to incorporate in the device a cross slide structurewhich will feed transversely of a main slide that moves longitudinallyof the work piece, with the cross slide structure being advancedtransversely to progressively greater depths into the thread grooveformed in the work, during successively following passes of the mainslide longitudinally of the work.

It is further proposed that when the device is used for a special orsingle purpose, such as a continuous run on an automatic machine, a camtype traverse would be used and in this event the feed cam would be sodesigned that it would need no manual setting.

A further object is to provide manually settable means, capable of beingcalibrated as desired, for presetting the cross slide structure inrespect to the depth of the groove to be formed in the work, with thestructure thereafter being self-feeding radially inwardly of the'work onsuccessively following passes of the main slide.

Another object is to incorporate an electro-mechanical means forcontrolling the cycle of operation of the machine, unless a cam traverseis used.

In the instant invention, the device is made with the lead screw as themeans for effecting traverse of the main slide. However, a model couldbe made with a cam traverse. The cam would'be so designed that thechasing tool would cover the same path at every stroke. Such a designmay be entirely satisfactory for various applications of the invention.In other instances, a traverse of the type illustrated and describedherein may be employed. Thus, the cam traverse design as embodied in anactual working model, has been found entirely satisfactory except forthe following:

(1) With a cam giving a traverse of two-inches, much time is lost onshort threads; and

(2) If different cams were used, the time of changing cams would be anobjection as well as their cost. Multiple lobe cams would not involvechanging of gears other than those required for different threads.

In this connection, a three inch cut is about the maximum practical andthis has been found entirely satisfactory for most thread chasingoperations. The lead screw arrangement illustrated and described hereinpermits one to change the length of the stroke readily, and all that isnecessary is to change the location of a bridge which will also bedescribed in detail, by adjusting the bridge position longitudinally ofand along the ways of the base. In this way, the device illustrated anddescribed herein can cut a thread approximately seven inches long.

Still another object is to provide a machine as described that will beparticularly accurate in respect to the thread-chasing operationsperformed thereby, will be capable of manufacture at comparatively lowcost considering the benefits to be obtained from its use, and.

will be rugged and substantially trouble-free in operation.

A further object is to include novel means including first and secondcross slide members connected by a.

toggle linkage, in a manner such that at the completion of each passmade by the main slide longitudinally of the work, the bit will beautomatically retracted, and will be subsequently fed into the work onceagain on the initiation of the next cycle of operation.

Still another object is to incorporate, in the cross slide structurereferred to immediately above, means for pre positioning one of theslides, so as to provide, in elfect, an adjustably positioned base pointfrom which the toggle linkage is extended, to locate the bit at aselected, ad-- justed depth relative to the work.

For further comprehension of the invention, and of the objects andadvantages thereof, reference will be had to the following descriptionand accompanying drawings, and to the appended claims in which thevarious novel features of the invention are more particularly set forth.

In the accompanying drawings forming a material part of this disclosure:

FIG. 1 is a top plan view of a thread-chasing apparatus according to thepresent invention, parts being broken away.

FIG. 2 is a side elevational view thereof, a portion of the adapterbeing broken away, shown in section.

FIG. 3 is a transverse sectional view on line 33 of FIG. 1.

FIG. 4 is a transverse sectional view on line 4-4 of:

FIG. 1.

FIG. 5 is a transverse sectional FIG. 1.

FIG. 6 is a transverse sectional View on line 6-6 of FIG. 1.

FIG. 7'is a sectional view through the thread-chasing bit holder,substantially on line 77 of FIG. 6.

FIG. 8 is a horizontal section, online 8-8 of FIG. 6.

view on line 55 of FIG. 9 is a wiring diagram showing the circuit of theother portions being.

stituting the present invention has to be positioned in reference to thework piece. Means for positioning the same would be on the largermachine, such as a lathe, to which the device is attached. If the deviceis incorporated in a larger machine, the machine would need a spindle,means for driving it at various speeds, gear changes for differentthreads, ways for longitudinal and transverse movements and a connectionfrom the machine spindle to the lead screw of the thread chasing deviceconstituting the present invention. When once positioned for the sametype of work piece, the machine constituting the present inventionremains fixed unless the larger machine on which it is mounted is alsoperforming other operations on the same work, in which case the threadchasing attachment could quickly be positioned by means of stops orgraduations on the moving parts.

Adapter 10, at its upper end, is connected rigidly to a flat base 12,said base being formed with a longitudinally extending, wide, dovetailtongue 14.

It would be understood that the device would be used largely as anattachment, and thus would be so designed as to fit different types ofmachines in most commercial embodiments of the device. Accordingly, itis for this reason that an adapter 10 is used. All attachments would bemade to the base 12 of the device, or to the main slide or bridgedescribed hereinafter, so that the only requirement for fastening thedevice to any type of machine would be the adapter, unless a camtraverse is used.

Machines of the same type and make would have different distances fromthe cross slide to the spindle center so that no adapter would fit morethan one type and size of machine.

A bridge 16 extends transversely of the base, fully from side to sidethereof, as clearly shown in FIG. 1, said bridge at one side projectinglaterally outwardly of the base a short distance.

The bridge 16 has been shown to particular advantage in FIGS. 1, 3 and4, and as shown in FIG. 4, is formed formed on its underside with adovetail groove 18 receiving the tongue 14. The bridge 16 is thus bodilyadjustable in a direction longitudinally of the base, to selectedpositions upon the base. In each position to which the bridge isadjusted, it may be fixedly secured on one side, as for example byscrews 20 (see FIG. 4) threadedly engaged to bear against a gib. Eventhough the main slide and the cross slide may be of relatively lightweight material such as aluminum, the weight thereof is such that whenthe parts are returning at high velocity, the impact must be absorbedlargely by the screws 20 at the side of the bridge and hence, screws ofsubstantial size are desirable. Other means might be employed, designedto obtain the same result of permitting adjustment of the bridge andfixed connection of the same to the base in a selected position ofadjustment.

Secured to the bridge at one end thereof (see FIG. 3) is a switch 22,which can be, per se, completely conventional. Switch 22 can be anormally closed micro-switch or the equivalent, and has an outwardlyspring-pressed movable switch contact 26 and an elongated arm 28pivotally mounted at 27 on the housing of the switch in the path ofmovement of a device carried by the main slide.

Designated generally at 30 is a main slide, including a plate-like slidebody 32, said main slide being formed, as shown in FIG. 6, with adovetail groove 33 receiving base 12.

At the end of the main slide, adjacent bridge 16, there is integrallyformed upon the main slide, medially between opposite sides thereof, anupwardly projecting, approximately semicircular, transversely extendinglip 34 (FIGS. 1 and Adjacent one side of the lip, there is formedtherein a threaded opening in which is engaged a screw 36 (FIG. 1),adapted to engage a movable lug or button 38 of a switch provided uponthe bridge 16 to actuate the switch.

A belt 40 is extended through an opening 41 formed in the bottom edge ofbridge 16 (FIG. 4), and is secured to the main slide at the location oflip 34. Belt 40 is trained about a vertically disposed pulley or roller42 (see FIG. 2), rotating in a vertical plane in a longitudinal slot 44formed in the base adjacent bridge 16 (FIG. 1). The pulley 42 has a stubaxle 46 rotating in bearings 48 of a pulley bracket 49 fixedly securedto the base.

Belt 40 is extended downwardly from the pulley 42, and at its lower endis secured to the bifurcated end 23 of a vertically disposed bolt 43that extends downwardly within a large opening of a vertically elongatedweight 50 of oblong cross section. Bolted to the top surface of theweight 50 is a crossbar 45, that covers the upper end of the bore 47 ofthe weight.

The lower end of the bolt 43 is threaded, and threadedly engaged withthe bolt and adjustable longitudinally thereof is a disc or washer 31,against which abuts a compression, coil spring 39. Spring 39 extendswithin bore 47, and at its upper end abuts against the crossbar 45. Bolt43 is freely slidable in a center opening 35 of the crossbar.

Guide rods 37 are fixedly secured at their upper ends to the bracket 49,the guide rods being loosely positioned through guide openings 29 of thecrossbar. The rods are threaded at their upper ends and carry adjustingnuts 37'.

As a result, when the main slide to which the belt is connected isshifted toward the right in FIG. 2, the weight is pulled upwardly, withthe belt traveling upwardly and to the right in FIG. 2 about the pulley42. Ultimately, the crossbar 45 will engage the nuts 37' preventing anyfurther upward movement of the weight. As the traverse of the main slidecontinues in a direction toward the right in FIG. 2, the disc 31 willnow begin to move upwardly with the bolt 43, Within bore 47 of theweight, and spring 33 will begin to compress more and more.

As a result, the pressure on the strap or band will be greater than thatexerted by the weight ordinarily, so as to insure a proper returnmovement of the main slide and prevent excessive impact upon the bridgethat would tend to otherwise loosen the bridge.

The weight is not heavy enough on short strokes to retract themechanism. However, on long strokes it will carry the slide back withsufficient speed once it is started.

Adjustment of the spring pressure may be regulated for differentconditions by changing the location of the nuts 37' to selectedpositions downwardly from the bracket, so that the location at which theweight is engaged against further upward movement can also be adjustedto initiate compression of the spring. A crossbar below the weight willpick it up on long strokes and take off the load if the velocity is toogreat.

A radial lug or block 52 is fastened to the belt 40 and carried aroundthereby.

Lug 38 constitutes a movable switch contact, it being understood thatthe switch associated with lug 38 may be engaged in a suitable recessprovided in the bridge 16, said switch being somewhat diagrammaticallyrepresented at 53 in FIG. 1. Switch 53 is normally open, being closed byclosing movement of the lug 38 by screw 36 carried by the main slide,when the main slide 30 is moved to the maximum extent to the left inFIG. 1, to its initial or starting position shown in this figure of thedrawing.

In any event, a solenoid contactor or relay 54 is mounted upon the mainslide, for a purpose to be made presently apparent. The contactor issimply an electrically operated device.

Threadedly engaged in the bridge 16 is a screw 56, having a reduced,elongated axial extension 58, the distal end of which is rounded off,said extension providing an adjustable stop for a toggle linkage to bedescribed in detail hereinafter.

Adjacent the screw 56, bridge 16 carries a pivoted,

spa e 1o sleeve extension 6d at one side thereof, and (see FIG. 4) aknurled adjusting sleeve 62, formed with internal threads and rotatablyengaged in a complementary recess 63 of extension 66, receives anelongated, threaded stem ea, thus to shift the stem 64 in an axialdirection without rotation of the same, responsive to rotatable movementof the knob or sleeve 6'2.

At its free end, the stem 64 is formed with a sharpened tooth as (seeFIG. 1), thus to provide a pawl.

The pawl is swingably mounted, since the sleeve 60 is pivoted on thebridge by means of the screw or pivot pin 68. in this connection, aspring means would be provided, in a commercial embodiment tending tohold the pawl 66 in engagement with the ratchet, so that the pawl willremain in contact with the ratchet wheel in any of various positions towhich the ratchet wheel may be shifted transversely of the main slideduring operation of the machine. The pawl 66 pushes the ratchet wheelaround.

An auxiliary or cross slide assembly includes a cross slide base 70which, as shown in FIG. 7, is of channeled formation, having a guideway72.

it will be understood that the cross slide base could be pivoted on themain slide on the same center as the back pivot stud when the auxiliaryslide is retracted. It might be positioned by screws extending into themain slide with the base at an angle of 90, 76 or 61 with the main slideas desired. This would allow cutting of a square thread, an acme thread,or a V thread respectively, although all threads might be cut at 90.Ninety degrees is the only angle at which a square thread can be cut andchasing is the only method used in cutting a square thread.

In the illustrated example, the cross slide base 7% is rigid with themain slide 32. It could be secured to the main slide, as for example, bybolts, and in fact, could be pivotally adjustable upon the main slideabout a ventical axis perpendicular to the length of the cross slide. Inthe illustrated example the cross slide base is fixedly secured to themain slide in a position in which its length is inclined slightly out ofperpendicularity to the length or path of movement of the main slide.The channel or slide base 7t} could be otherwise arranged, of course,andmight be exactly perpendicular to the length of the main slide, or atsome angle of inclination other than that shown in FIG. 1.

in any event, at its opposite ends, the guide channel or trackway '72 isclosed by end plates 74, 76 which extend transversely of the slide base70 and are bolted in place, to the body of the slide base.

Forward. plate '74 serves to seat one end of a pair of compressionsprings that will be described hereinafter, there beingv slight recessesin the plate 74 for this purpose. The rear plate 76 takes the thrust ofa cam to be hereinafter described, and as will be noted from FIG. 8,plate 76 has a notch into which the cam retracts in one position of thecam.

Slidably engaged in the channel 72 are first and second cross slides 78,86, respectively (see FIG. 8). The cross slide 78 carries a bit supportblock 82 secured thereto by screws 86, said block 82 having a coverplate 84 (see FIG. 7 Smooth-walled, registering openings of cover plate84 and block 82 are in registration with threaded, upwardly openingrecesses of the slide 78, and accordingly, the cover plate can beengaged in place, cooperating with the body of the block 82 in clampablyengaging a bit 33. Bit 38 is of any desired cross-sectional shape, andin the illustrated example is of rectangular section, with the coverplate and body having confronting, endto-end channels in which the bitis clamped. The bit is adapted to form threads in a work piece 90 whichwould besuitably held adjacent the device constituting the presentinvention, and which would be rotated simultaneously with thelongitudinal advancement of the main slide along the tongue 12. Holdingthe bit securely in place are clamping-screws 92 threadedly engaged in.the,

cover plate.

The first or bit support slide 78 is movable outwardly as viewed in FIG.1, and when it has reached the limit of.

its outward movement, that is, when the free or workengaging end of thebit is at the depth of the thread grooves formed in the work 9%, meansis provided to re-- tract the slide 78. This includes a pair ofcompression springs 94, one end of which are seated in recesses 75 inplate 74 and the other end in recesses 96 in the cross slide.

Referring now to FIGS. 1 and 6, a pin 93 threadedly engages in the rearend of slide '78, and passes through an opening formed in one end of atoggle link 100, the other end of which is overlapped with and pivotallyconnected to a second toggle link 162 by means of a pin 104. Link 1%pivots on pin 98, and link 102, as shown in FIG. 6, has a pivotalconnection to the slide 80, provided by a vertically elongated pin 1'66,threadedly engaged in slide and extending within a bushing 108 which isfree to rotate on pin 1% and which is keyed at 110 to a hand knob 112, aratchet wheel 114, and a cam 116. Link Hi2 and bushing 188 arerelatively rotatable.

Stud or pin 1% (see FIG. 6) has adjacent its base portion a collar orshoulder W7, which reduces the thickness of the cam 116, and whichspaces the cam away from the slide 30. This increases the strength ofthe stud at this location.

Slide 80 is only half the height of slide 78, or stated otherwise, isonly half the depth of the groove 72. The remaininghalf of the depth ofthe groove is occupied by the cam 116 and shoulder 197 so that the topsurface of the cam is flush with the top surface of the slide base '70.Links rec, 102 are in contact with said top surfaces of cam 116 andslide 78.

Referring to FIG. 8, earn 116 has a spiralling periphery, producing apronounced step 113 where the portion of the periphery, that is, at thegreatest distance radially from the axis of the cam meets that portionof the periphery which is at the smallest distance in the samedirection. In other words, the feed is rapid at the start and graduallygrows less and less rapid until at the last 15 the curve is concentricwith the center of the cam rotation.

In FIG. 1 the toggle links are shown in longitudinal. alignment, thatis, the toggle is straightened out. The links, however, are adapted tobe angularly related, with. the connecting pin T04 of the toggleshifting in the direction of the arrow shown in FIG. 1, to the left inthis figure of the drawing.

Limiting swinging movement of the toggle links me, 162 in respectivelyopposite directions are abutments mounted upon opposite sides of thechannel 72. These abutments include ears 12%, having threaded openingsin which are engaged screws 122. The abutments are thus adjustablelaterally inwardly of the channel, with one screw being adapted toengage link and the other screw being disposed at the opposite side ofthe toggle and being adapted to engage link 1432'.

At one end of the base, there is fixedly mounted upon the base anupwardly projecting abutment support memher 124, having a threadedopening in which is engaged a screw 126 formed with a reduced, axialextension 1128- disposed in the same vertical plane with extension 58 ofscrew 56 (see FIG. 1). The axial extensions I28, 58 form abutments atopposite sides of the toggle, engaging correspondingly opposite sides ofthe link 162 during movement of the main slide through its workingstroke and return stroke respectively, that is, its movements first tothe right in FIG. 1 and then to the left in the same figure of thedrawing.

A lead. screw 134 is journalled in bearings 13%) and 132 on the ends ofthe base 12. The lead screw must be driven by the same source of poweras the drive spindle to which the work piece is attached. The two mustbe positively geared together by gears to give the exact.

desired ratio between the r.p.m. of the spindle and the rpm. of the leadscrew with no chance for slippage.

Referring to FIG. 5, in embracing relation to the screw, but completelyout of contact therewith, is a U-shaped supporting bracket 136 fixedlysecured to the main slide 30 for movement therewith longitudinally ofthe screw. Supporting bracket 136 has its outer leg secured to asupporting arm sectionally constituted by members 138, 140 fixedlysecured to each other and extending longitudinally of the screw as shownin FIG. 1. To the forward end of the member 140 there is secured theinner end of a laterally outwardly projecting U-shaped bracket 142 onwhich is mounted a solenoid 144, the core of which projects toward thescrew. Secured to the projecting end of the core is a half-nut 145,threaded complementarily to screw 134. When the solenoid is energized,the core thereof is projected outwardly to engage the half-nutthreadedly with the screw 134.

The adapter is used to attach the device to a ma chine and as previouslynoted herein, all portions or components of the device must be fastenedto or above the base, which is a relatively thin piece as seen from theside. The controls may be attached to a projecting plate or shelf castintegral with the main slide and this plate would provide ample room formounting the limit and opening switches one above the other and acommutator above or on the shelf. Of course, the commutator shaft passesthrough the shelf in such an arrangement to hold the teeth of the gearcarried thereby in contact with the lead screw. Secured under the shelfand to the same would be the holding switch, the relay or contactor, andthe solenoid.

The solenoid would be of the push type and pushes the half-nut intocontact with the lead screw. Various arrangements might be employed,alternatively. For example, it might be decided to use two half-nuts asin a lathe, in which case a link connection would be used. When thehalf-nut is pushed in it compresses a spring (not shown) which wouldpull the half-nut out of engagement when the solenoid is deenergized, atthe end of the cutting stroke.

Adjacent the bearing projection 132, a gear wheel 148 is in mesh withthe screw 134, and rotates on an axis perpendicular to that of thescrew. The gear wheel 148 is keyed or otherwise secured to a pin 146which projects above the gear wheel as seen in FIG. 2, and which alsohas a reduced extension extending below the gear and rotatably bearingin a vertically extending bearing sleeve 150 fixedly mounted upon abracket 152 that is fixedly attached to one side of the base.

Referring to FIG. 2, the pin 146 is of non-electrically conductivematerial, as for example plastic, and embedded in the surface of the pinand extending longitudinally of the pin, above gear 148, is bridgingelement 154 of electrically conductive material, bridging springcontacts or brushes 156, 158 that are anchored to the base. The pin andelement 154 constitute a commutator.

The invention contemplates use of a limiting switch 164, normally closedand an opening switch 166, normally closed, mounted on a stationaryportion of the base. These switches are shown diagrammatically in FIG.9, and are actuated by adjustable screws 168 and 170, respectively,carried on an extension of support 124.

Referring to FIG. 9, the electric current flows from the main or housesupply to the normally closed limit switch 164 to opening switch 166.Switch 166 will be closed after main slide '30 begins to move back afteropening the circuit momentarily at the normal end of the stroke. Fromswitch 166 the current passes through two circuits. One circuitincluding the switch 53, brush 156, commutator 146, brush 158, to relaycoil 162 to the source. Energization of the coil 162 provides thesolenoid 144 with some initial movement. This initial movement of thesolenoid closes the holding switch 135 and the current will pass throughsaid switch 135, relay 54 holding the switch of the relay closed andallowing the main slide carrying the solenoid 144 to complete its strokewhen the actuating screw opens switch 166.

The circuit is such that the half-nut will be permitted to engage thethreads of screw 134- only when the threads of the half-nut are inexact, meshing relation to the threads of the lead or advancing screw.This is the purpose of commutator or brush-type electrical contactprovided by the geared dial 148. The principle is the same that used onmodern engine lathes. In other words, even though the circuit might beotherwise closed, the half-nut is not permitted to move into engagementwith the threads of the screw 134 unless and until the contacts 156, 158are bridged by the element 154. They will be so bridged, of course, onlywhen the gear 148 is in a predetermined position relative to the leadscrew and at this particular time, the half-nut can be advanced intoengagement with the threads of the lead or advancing screw.

In any event, in operation of the device, it will be assumed that thework piece has been advanced to the proper position, and is rotating.The main slide 30, thus, in FIG. 1 is in its initial or startingposition, with the contact 38 of switch 53 engaged by screw 36.

At this time, the knob 112 is manually rotated to rotate cam 116 to aselected position with its cam face; in en agement with the rear plateor end plate 76 (FIG. 8) so that plate 76 is forced inwardly. Thisadjustably locates the slide 80, and in turn causes a correspondinglyadjusted location of the slide 78 for initial operation. When the mainslide 30 reaches its initial or starting position, the free end of theabutment pin 58 engages link 162, straightening out the toggle andthereby causing slide 78 to be advanced to a greater extent than slide80, advancing the bit a selected extent into engagement with the work.There is thus a rigid connection between plate 76 and the work piece 90thereby maintaining the links and 102 in straightened condition. Switch53 is closed at this point, by depression of the contact 38, andassuming that the contacts 156, 158 are bridged, solenoid 144 isenergized. The half-nut engages screw 134, and as a result the mainslide is shifted to the right in FIG. 1.

Since the work piece 90 is rotating, this produces a helical thread inthe work piece.

As the slide finishes its return stroke, the links are straightened out,with the operation being finished just at the end of the stroke. Thetoggle 100 at the end of each pass is straightened by pine 56 andbrought to bear against the adjusting stop or screw 122, the positionbeing such as related to the central pivot pin 104 to move it just pastcenter, the return springs 84 pressing against the cross slide 14 andholding the toggle members rigidly in line until the pin 126 engages thetoggle at the end of the stroke and causes the toggle to collapse, thusretracting the cross slide.

Eventually, when the thread has been completed to the desired extent,the abutment pin 128 will engage the right-hand side of link 102,viewing the same as in FIG. 1. At the end of each forward stroke theopener or pin 128 will open the toggle. The cutting tool must be movedcompletely out of the thread or cross threading will result in spoilingthe thread on the return stroke. This will cause the links 100, 102 tomove into an angular relationship to one another. As a result, slide 78will be retracted, moving the bit out of engagement with the work in adirection radially outwardly from the work.

At the same time, as the main slide finishes its travel on the cuttingstroke, the lug or block 52 on belt 40 will engage arm 28 of switch 22.This will cause the arm to be rocked, opening the normally closed switch22. This will temporarily open the circuit through the solenoid, so thatthe core of the solenoid retracts, disengaging the half-nut from thescrew 134, whereupon the pull of the weight 50 on belt 40 willaccordingly cause the main slide 30 to be returned to its initial,starting position, and when it reaches said position, switch 53 willagain be closed by.

screw 36 engaging switch button 38, starting the cycle all over again.

The construction is designed to insure progressive advancement of thebit radially inwardly of the work, during successive passes along thethreads. This provides for more accurate threading of the work and for acleaner thread groove. The design is such that the first cut,particularly for a V-type thread, should be relatively deep, as theamount of metal removed for a given feed is smaller than in later cutswhere the width of the cut materially increases. Further, at this stage,finish is unimportant. The knob 112 is rotated manually to reset thetool at the end of each complete thread or the beginning of a new one toadjust the depth of the thread. It is often desirable to have thefinishing cuts relatively light with perhaps the final pass being madewithout any feed, to insure a smooth finish thread. From start to finishof a complete thread including the individual passes, the operation iscompletely automatic.

The cam 116, acting in conjunction with the ratchet wheel 114 and thepawl 66, accomplishes this operation. The function of the pawl 66 is toengage the desired number of teeth of the ratchet wheel 114 near the endof the return stroke, rotate the wheel and the feed cam 116, the desireddepth for the ensuing cut, and repeat this operation for each stroke,until the thread is cut progressively deeper, until completed when adeep cut in the cam 116 will allow the slide to retract by pressure ofspring 94. The slide 80 and hence the slide 78 are initially set byrotation of the knob 112, at the end of each complete thread or at thebeginning of a new thread, moving slide 80 a selected distance away fromthe end plate 76 to a pre-fixed stop. The knob may however be rotatedagainst an adjustable stop for quick action and if required for longruns the setting could also be automatic. On each pass, over the samethreads of work piece 90, a deeper cut is to be made. Accordingly, eachtime the main slide is moved through its return stroke back to itsinitial, FIG. 1 position, the pawl 66 will be brought into engagementwith the ratchet wheel 114, turning said ratchet wheel through a givennumber of degrees. Cam 116 is, accordingly, correspondingly turned.Therefore, the cam will be progressively moved to successively followingpositions in which its periphery is at a greater radial distance fromits axis. This causes a corresponding, progressive movement of slide 80toward the work piece. Slide 78 is therefore correspondingly moved, oneach pass of the work, slightly closer to the work piece Eventually, asthe cam reaches the position shown in FIG 8, the periphery of the camremains at a constant radius from the axis of the cam, rather thancontinuing in its spiral. The final pass is thus made without anyfurther feed of the bit into the work, to clean out the threadpreviously formed in the work. Then, on the next pass, the cam moves toa position in which its abutment or step 118 shifts away from theadjacent end plate, bringing the low end of the peripheral cam surfaceinto engage- 10 ment with the thrust or end plate to retract the slideand slide 78 to their initial position for acting on another work piece,which may be automatically moved into position simultaneously withremoval of the work piece previously finished.

It will be understood that in some commercial embodiments, it may bedesired to use a cam traverse, which would be better than the lead screwillustrated, for certain conditions.

While I have illustrated and described the preferred embodiment of myinvention, it is to be understood that I do not limit myself to theprecise construction herein disclosed and that various changes andmodifications may be made within the scope of the invention as definedin the appended claims.

Having thus described my invention, what I claim as new, and desire toto secure by United States Letters Patent is:

1. In a thread-chasing apparatus having a base and a carriage slidableon the base, mechanism for effecting reciprocation of the carriage,comprising a feed screw supported on the base, a half-nut follower onthe carriage having threads engageable with threads of the feed screwduring rotation of the feed screw and when the threads of said feedscrew and half-nut are in alignment, a solenoid on the carriage having acore mounting the half-nut for extension of the half-nut into and out ofengagement with the feed screw responsive to energizing and deenergizingof the solenoid, a commutator driven in timed relation by the feed screwand switches in circuit with the solenoid controlled by said commutatorfor energizing and deenergizing the solenoid, said commutator having abridging element completing the circuit of said solenoid.

2. In a thread-chasing apparatus having a base and a carriage slidableon the base, a mechanism according to claim 1 further comprising switchmeans in circuit with the solenoid and operable responsive to movementof the carriage to opposite ends of its path of reciprocation, saidswitch means being adapted for energizing the solenoid at one extremelimit of movement of the carriage and for deenergizing the solenoid atthe other extreme limit of the carriage movement, said switch meansincluding one switch, said one switch being mounted on said base andincluding a switch contact, and a lug on the carriage engageable withsaid contact to operate said one switch when the carriage reaches oneextreme limit of its travel.

References Cited in the file of this patent UNITED STATES PATENTS2,527,397 Castelli Oct. 24, 1950 2,565,020 Christman Aug. 21, 19512,581,082 Drissner Jan. 1, 1952 2,622,252 Wernli Dec. 23, 1952 2,778,037Renoux Ian. 22, 1957 FOREIGN PATENTS 346,617 Great Britain Apr. 16, 19311,073,701 France Mar. 24, 1954

